Design and implementation of a pem fuel cell emulator for static and dynamic behavior

This paper presents the design, implementation, and experimental validation of a digitally-controlled emulator of proton exchange membrane (PEM) fuel cells for static and dynamic behavior. The emulator is a low cost, easy to use, and portable device designed to evaluate power systems and control strategies for fuel cell-based generation systems. For the implementation of this emulator, an appropriate mathematical model is chosen, parameterized, and experimentally validated. The resulting model is processed digitally by the emulator, which generates the appropriate electrical behavior to a load. The emulator power stage is implemented by using a two-inductor step-down DC/DC switching converter, which is controlled directly by the digital processing system. Later, the electrical scheme of the power stage and the block diagram of the system are presented, and the behavior of the emulator is illustrated with a simulation. Finally, the emulator is validated using experimental data

Aplicação da técnica MPPT para otimização de energia convertida em sistema de geração a partir do movimento de ondas oceânicas

Este trabalho tem como objetivo apresentar a aplicação de um método para obtenção de uma maior eficiência energética em um sistema de geração de energia elétrica a partir do movimento de ondas oceânicas. Inicialmente, é exposto um estudo dos sistemas já existentes de conversão de energia das ondas marítimas e oceânicas através da apresentação de diferentes classificações e modelos desenvolvidos nas últimas décadas por pesquisadores desta área, não usualmente explorada, mas que vem ganhando espaço devido a sua potencialidade. Em seguida, é apresentado o método MPPT, foco do trabalho, mostrando e classificando as diferentes formas de rastrear-se e obter-se o ponto de máxima potência na conversão de energia elétrica, comumente utilizado na geração eólica. Assim, é aplicado este método em um conversor de energia elétrica projetado para um sistema de coluna de água oscilante, composto por um gerador síncrono trifásico de imãs permanentes e um retificador PWM trifásico e seus controladores que atuam para manter o fator de potência unitário e para ter baixos níveis de distorção harmônica. Considera-se neste trabalho uma geração de energia elétrica oriunda de uma boia em alto-mar, chamada de spar buoy, capaz de alimentar um banco de baterias que armazenará carga suficiente para alimentar sensores de monitoramento climático. A aplicação do método MPPT tem sua relevância neste tipo de sistema, uma vez que as condições de amplitude e frequência das ondas variam de modo intermitente. É utilizado o método MPPT com o princípio Perturba e Observa a fim de validar sua usabilidade para esta aplicação. Para tal, através de um simulador de circuitos elétricos, são realizadas simulações onde o método MPPT buscará a melhor referência para os controladores do sistema operando em diversas condições. Assim, são apresentadas as curvas de saída de potência, curvas de tensão e corrente no gerador, que comprovam a eficiência do MPPT para este tipo de sistema de conversão estudado.This work aims to present an application of a method to obtain greater efficiency in an electrical energy generation system from the movement of ocean waves. Initially, a study of the already existing sea and ocean waves energy conversion systems of is presented through the presentation of classifications and models developed in the last decades by research in this area, not usually explored, but which has been gaining space due to its potential. Then, the MPPT method, the focus of the work, is presented, showing and classifying how different ways to track and obtain the maximum power point in the conversion of electrical energy, commonly used in wind generation. Thus, this method is designed in an electrical energy converter designed for an oscillating water column system, composed of a three-phase permanent magnet generator and a three-phase PWM rectifier and its controllers that act to maintain the unity power factor and to have low levels of harmonic distortion. In this work, it is considered a electrical energy generation from an offshore buoy, called a spar buoy, capable of supplying a bank of batteries that will store enough charge to supply climate monitoring sensors. An application of the MPPT method has its nature in this type of system, as the conditions of amplitude and frequency of waves vary intermittently. The MPPT method with the Disturbance and Observation principle is used to validate its usability for this application. For that, through an electrical circuit simulator, simulations are carried out where the MPPT method seeks the best references for the system drivers operating under different conditions. Thus, power output curves, voltage and current curves in the generator are presented, which prove the efficiency of the MPPT for this type of conversion system studied

Performance Analysis of Photovoltaic Fed Distributed Static Compensator for Power Quality Improvement

Owing to rising demand for electricity, shortage of fossil fuels, reliability issues, high transmission and distribution losses, presently many countries are looking forward to integrate the renewable energy sources into existing electricity grid. This kind of distributed generation provides power at a location close to the residential or commercial consumers with low transmission and distribution costs. Among other micro sources, solar photovoltaic (PV) systems are penetrating rapidly due to its ability to provide necessary dc voltage and decreasing capital cost. On the other hand, the distribution systems are confronting serious power quality issues because of various nonlinear loads and impromptu expansion. The power quality issues incorporate harmonic currents, high reactive power burden, and load unbalance and so on. The custom power device widely used to improve these power quality issues is the distributed static compensator (DSTATCOM). For continuous and effective compensation of power quality issues in a grid connected solar photovoltaic distribution system, the solar inverters are designed to operate as a DSTATCOM thus by increasing the efficiency and reducing the cost of the system. The solar inverters are interfaced with grid through an L-type or LCL-type ac passive filters. Due to the voltage drop across these passive filters a high amount of voltage is maintained across the dc-link of the solar inverter so that the power can flow from PV source to grid and an effective compensation can be achieved. So in the thesis a new topology has been proposed for PV-DSTATCOM to reduce the dc-link voltage which inherently reduces the cost and rating of the solar inverter. The new LCLC-type PV-DSTATCOM is implemented both in simulation and hardware for extensive study. From the obtained results, the LCLC-type PV-DSTATCOM found to be more effective than L-type and LCL-type PV-DSTATCOM. Selection of proper reference compensation current extraction scheme plays the most crucial role in DSTATCOM performance. This thesis describes three time-domain schemes viz. Instantaneous active and reactive power (p-q), modified p-q, and IcosΦ schemes. The objective is to bring down the source current THD below 5%, to satisfy the IEEE-519 Standard recommendations on harmonic limits. Comparative evaluation shows that, IcosΦ scheme is the best PV-DSTATCOM control scheme irrespective of supply and load conditions. In the view of the fact that the filtering parameters of the PV-DSTATCOM and gains of the PI controller are designed using a linearized mathematical model of the system. Such a design may not yield satisfactory results under changing operating conditions due to the complex, nonlinear and time-varying nature of power system networks. To overcome this, evolutionary algorithms have been adopted and an algorithm-specific control parameter independent optimization tool (JAYA) is proposed. The JAYA optimization algorithm overcomes the drawbacks of both grenade explosion method (GEM) and teaching learning based optimization (TLBO), and accelerate the convergence of optimization problem. Extensive simulation studies and real-time investigations are performed for comparative assessment of proposed implementation of GEM, TLBO and JAYA optimization on PV-DSTATCOM. This validates that, the PV-DSTATCOM employing JAYA offers superior harmonic compensation compared to other alternatives, by lowering down the source current THD to drastically small values. Another indispensable aspect of PV-DSTATCOM is that due to parameter variation and nonlinearity present in the system, the reference current generated by the reference compensation current extraction scheme get altered for a changing operating conditions. So a sliding mode controller (SMC) based p-q theory is proposed in the dissertation to reduce these effects. To validate the efficacy of the implemented sliding mode controller for the power quality improvement, the performance of the proposed system with both linear and non-linear controller are observed and compared by taking total harmonic distortion as performance index. From the obtained simulation and experimentation results it is concluded that the SMC based LCLC-type PV-DSTATCOM performs better in all critical operating conditions

POWER CONDITIONING UNIT FOR SMALL SCALE HYBRID PV-WIND GENERATION SYSTEM

Small-scale renewable energy systems are becoming increasingly popular due to soaring fuel prices and due to technological advancements which reduce the cost of manufacturing. Solar and wind energies, among other renewable energy sources, are the most available ones globally. The hybrid photovoltaic (PV) and wind power system has a higher capability to deliver continuous power with reduced energy storage requirements and therefore results in better utilization of power conversion and control equipment than either of the individual sources. Power conditioning units (p.c.u.) for such small-scale hybrid PV-wind generation systems have been proposed in this study. The system was connected to the grid, but it could also operate in standalone mode if the grid was unavailable. The system contains a local controller for every energy source and the grid inverter. Besides, it contains the supervisory controller. For the wind generator side, small-scale vertical axis wind turbines (VAWTs) are attractive due to their ability to capture wind from different directions without using a yaw. One difficulty with VAWTs is to prevent over-speeding and component over-loading at excessive wind velocities. The proposed local controller for the wind generator is based on the current and voltage measured on the dc side of the rectifier connected to the permanent magnet synchronous generator (PMSG). Maximum power point tracking (MPPT) control is provided in normal operation under the rated speed using a dc/dc boost converter. For high wind velocities, the suggested local controller controls the electric power in order to operate the turbine in the stall region. This high wind velocity control strategy attenuates the stress in the system while it smoothes the power generated. It is shown that the controller is able to stabilize the nonlinear system using an adaptive current feedback loop. Simulation and experimental results are presented. The PV generator side controller is designed to work in systems with multiple energy sources, such as those studied in this thesis. One of the most widely used methods to maximize the output PV power is the hill climbing technique. This study gives guidelines for designing both the perturbation magnitude and the time interval between consecutive perturbations for such a technique. These guidelines would improve the maximum power point tracking efficiency. According to these guidelines, a variable step MPPT algorithm with reduced power mode is designed and applied to the system. The algorithm is validated by simulation and experimental results. A single phase H-bridge inverter is proposed to supply the load and to connect the grid. Generally, a current controller injects active power with a controlled power factor and constant dc link voltage in the grid connected mode. However, in the standalone mode, it injects active power with constant ac output voltage and a power factor which depends on the load. The current controller for both modes is based on a newly developed peak current control (p.c.c.) with selective harmonic elimination. A design procedure has been proposed for the controller. Then, the method was demonstrated by simulation. The problem of the dc current injection to the grid has been investigated for such inverters. The causes of dc current injection are analyzed, and a measurement circuit is then proposed to control the inverter for dc current injection elimination. Characteristics of the proposed method are demonstrated, using simulation and experimental results. At the final stage of the study, a supervisory controller is demonstrated, which manages the different operating states of the system during starting, grid-connected and standalone modes. The operating states, designed for every mode, have been defined in such a hybrid model to allow stability and smooth transition between these states. The supervisory controller switches the system between the different modes and states according to the availability of the utility grid, renewable energy generators, the state of charge (SOC) of energy storage batteries, and the load. The p.c.u. including the supervisory controller has been verified in the different modes and states by simulation